Naval History Forums

Just another question regarding trial displacement of warships vs. merchant ships.

I have been looking at different merchant ships and warships lately and have noticed that in their designs that are differences in the way that each type of ship will run its sea trials. Specifically, their different trial displacements in relation to their design displacement.

From what I have noticed, merchant ships tend to run their trials at displacements LIGHTER than their designed displacement; however, in warships, the situation is reversed, in that they run their trials HEAVIER than their designed displacement. Maybe this is due to the nature of each type of ship?

Most battleship and cruiser designs I have seen online would have run their trials at "around 10%" above their design displacements. One ship that blurs the line in this is the SS UNITED STATES, which is a hybrid, troopship/liner. But she fits in more of the merchant ship category than naval category, as far as displacement on trials go.

SS UNITED STATES - Merchant ship/troopship
Design displacement: 45,400 long tons
Design speed: 37.3 knots @ 240,000 SHP
Trial displacement: 40,000 long tons (39,900t on actual trials)
Trial speed: 38.32 knots @ 241,785 SHP

I believe the Italians (or possibly the French) ran their trials well below their standard displacement, which tended to give skewed results and make their ships look faster than they would normally have been in service (most likely for propaganda purposes).
Water depth in which the trials were run were also important, particularly in US and British service where a substantial bonus was frequently at stake if a new ship exceeded her specifications:

http://www.navweaps.com/index_tech/tech-091.htm